Medical Marijuana and Lung Cancer

The big question about marijuana smoke has always been, “Will it cause cancer?”  A review of the scientific literature still does not give a definitive answer but it appears that a leading and well known pulmonologist (lung specialist) from UCLA has found that marijuana is unlikely to cause cancer.  He has also determined that COPD (chronic obstructive pulmonary disease) is unlikely as well.  Dr. Donald Tashkin, Emeritus Professor of Medicine and Medical Director of the Pulmonary Function Laboratory at the David Geffen School of Medicine at UCLA, has been studying the effects of marijuana smoke since the 1970′s.  He was the lead investigator on the initial studies that identified the toxic components in marijuana smoke.  He also reported the  the studies that showed that there is damage from the smoke to the cells that line the upper airways of the lungs.  His findings have also found that marijuana smokers are more likely than non-smokers to have cough, sputum production, and wheezing.

The National Institute on Drug Abuse gave Dr. Tashkin a grant in 2002 to study if heavy, long-term marijuana smoking increases the risk of lung and upper airway cancers.  Dr. Tashkin and his associated looked at 2,252 patients, about half of which had cancer and half did not.  The patients were matched for age, gender, and neighborhood.  Marijuana use was measured in “joint years” which means the number of years that the patient had been smoking times the number of joints per day.

The results of this study showed that increased marijuana use did not result in higher rates of lung or throat cancer, but that the use of tobacco increased the risk of cancer.  Tobacco smokers who also smoked marijuana were at slightly lower risk of getting lung cancer than tobacco-only smokers.  Although the National Institute on Drug Abuse chose not to publish the results of this study, It was published in the October 2006 issue of the medical journal Cancer Epidemiology Biomarkers & Prevention.

There was a study out of New Zealand that got more attention that Dr. Tashkin’s study even though it only looked at a total of 79 patients, of which only 21 were cannabis users.  This study reported that heavy marijuana users (14 out of the 21 included in the study) had an increased risk of cancer; Dr. Tashkin himself stated that “one has to very cautious interpreting the results due to the very small number of cases.”